Power transmission devices may include a rack and pinion that converts a rotational motion into a linear motion or vise versa, and a gear train that converts a rotation speed and torque while transferring a rotational motion only.
In a typical case, a power transmission system of a power transmission device uses a pin gear mainly with a tooth shape based on an involute curve principle, sometimes with a tooth shape based on a cycloid curve principle.
The power transmission devices have been widely used for various industrial machines including semiconductor equipment, flat display equipment for LCDs, PDPs, OLEDs, etc.
FIG. 1 is a side view illustrating a configuration of a power transmission device according to the related art in a use state.
Referring to FIG. 1, the power transmission device 1 according to the related art may be partially coupled to a slider 3, for example, to allow the slider 3 coupled to a base plate 2 in a structure of a rail 4 to have a linear motion.
For the linear motion of the slider 3 with respect to the base plate 2, the power transmission device 1 connected to the slider 3 may include a pinion 6 that is engaged with a rack 5 fixed to an area of the base plate 2.
The pinion 6 is coupled to an end portion of a shaft 7 extending outwardly from the power transmission device 1 and engaged with the rack 5 during the assembly of the device of FIG. 1.
In the above structure, when a motor 8 of the power transmission device 1 is driven, the shaft 7 is rotated based on interactions of built-in parts of the power transmission device 1 and thus the pinion 6 is rotated.
As the pinion 6 is engaged with the rack 5 that is positionally fixed, the pinion 6 is consequently rotated, performing a linear motion along a lengthwise direction of the rack 5, thereby implementing the linear motion of the slider 3 with respect to the base plate 2.
Accordingly, when a desired part or apparatus is mounted on the slider 3, the part or apparatus may perform a linear motion.
The structure of the power transmission device 1 of FIG. 1 is one of the most used shapes at sites. Since the motor 8 is directly coupled to a rotation shaft of the pinion 6 with a decelerator 9, the overall height H1 of the power transmission device 1 may be increased.
When the overall height H1 of the power transmission device 1 is increased as in the related art, there may be a limit in the application of the power transmission device 1 to a compact apparatus.
For example, considering that it is difficult to apply the power transmission device 1 having a high height H1 as illustrated in FIG. 1 to a compact apparatus such as an index system (INDEX) that is widely applied to semiconductor equipment or flat display equipment, there is a demand for development of technology about a power transmission device that may have a reduced overall height H1 and may perform a stable operation.